1. Field of the Invention
The present invention relates to a clutch for a motor vehicle and, more particularly, to a clutch for a motor vehicle that has less transmission loss and that provides engine braking effect.
2. Description of the Related Art
Motor vehicles with continuously variable transmission generally utilizes centrifugal type clutches. FIGS. 9-11 shows a conventional centrifugal type clutch including a driving wheel 1′, an actuator plate 2′, a clutch hub 3′, and a shaft 4′. The driving wheel 1′ is driven by output of an engine via a belt 11′. The actuator plate 2′ rotates jointly with the driving wheel 1′ and includes a side plate 21′ to which a plurality of shoes 22′ is pivotably mounted. A friction plate 23′ is mounted on an outer face of each shoe 22′. The shoes 22′ are returned by springs 24′. The clutch hub 3′ is mounted around the side plate 21′ of the actuator plate 2′ and includes a disc 31′ and an annular wall with an inner peripheral friction section 32′ surrounding the shoes 22′. The disc 31′ includes a hole 33′ having spline grooves 34′ formed in an inner periphery thereof. The shaft 4′ is extended through the driving wheel 1′, the actuator plate 2′, and the clutch hub 3′. The shaft 4′ includes a spline section 41′ engaged with the spline grooves 34′. The shaft 4′ further includes a threaded end 42′ extending beyond the disc 31′ and engaged with a nut 43′. The shaft 4′ is connected to a wheel axle of a motor vehicle.
The output of the engine drives the belt 11′, the driving wheel 1′, and the actuator plate 2′ to rotate. With reference to FIG. 12, when the centrifugal force of the rotating actuator plate 2′ is larger than the returning force of the springs 24′, the shoes 22′ pivot outward so that the friction plates 23′ are in friction engagement with the inner peripheral friction section 32′ of the clutch hub 3′. Thus, the actuator plate 2′ can drive the clutch hub 3′, the shaft 4′, and the wheel axle to rotate, moving the motor vehicle forward while providing continuously variable transmission. However, slipping is liable to occur when the friction plates 23′ wear or the inner peripheral friction section 32′ is dirtied by dust and/or oil, leading to transmission loss.
Taiwan Utility Model No. M324138 discloses a centrifugal type clutch including first and second springs respectively for larger and smaller clutch plates to enhance the engaging force between a distal end of the larger clutch plate and the clutch hub. However, transmission loss still occurs.
Compared to lever type gear shifting, centrifugal type clutches provide smooth gear shifting and driving comfort. However, the centrifugal type clutches can not provide engine braking when the friction plates and the clutch hub are not rotating jointly. Thus, braking of downhill motor vehicles with centrifugal type clutches relies on the braking mechanism of the motor vehicles. Namely, the motor vehicles with centrifugal type clutches are not as safe as motor vehicles with lever type gear shifting.
Thus, a need exists for a clutch with less transmission loss while providing engine braking effect.